The present invention relates to a tread band applicator device operable to apply a tread band raw material mass onto a carcass of a tire to form thereon a tread band and, in particular, to form a tread band on the carcass of a tire having an especially long performance life.
A conventional tread band applicator device is described in FR-OS 23 59 700. This conventional tread band applicator device comprises a forming applicator which is connected to an extruder and is operable to apply a tread band raw material mass on the tire carcass. The application of the tread band raw material mass includes deposing a predetermined excess of the material mass onto the tire carcass, whereby a rubber roller is deployed to effect the filling of inadequately filled locations on the tire carcass.
A disadvantage of the just noted conventional tread band applicator device is that a special forming applicator configured with respect to the diameter of the tire to be handled must be used so that an inventory of different forming applicators for handling tires of differing diameters must be kept on hand.
The conventional tread band applicator device described in the above-noted publication may, however, fail to reliably completely fill the relatively deeper recesses in the tire carcass so that it is necessary, prior to the tread band applying process, to perform a labor intensive preparation of the tire with a small hand extruder in order to foreclose the possibility that air pockets and inadequately filled locations will remain in the tire to such an extent that the quality requirements of the tire retreader and its customers would not be met.
Additionally, the afore-described tread band applicator device is effective in its operation only within the range of applications in which the carcass diameter does not deviate substantially from a given diameter; otherwise, the tread bands applied in an application outside of this range will be markedly thick and/or markedly thin, either of which leads to unsatisfactory results upon vulcanization of the tire.
In order that the afore-described tread band applicator device can perform in a relatively satisfactory manner, it is additionally necessary that a relatively soft rubber mixture is used to form the tread band raw material mass. In such relatively soft rubber mixtures, the portion of solid particles is reduced; the traction of the retreaded tire formed therefrom is for the most part very good while, on the other hand, the performance life of the tire is decidedly short.
It must be noted, however, that, in view of the rising quality demands of customers, tires with a high performance life are increasingly in demand. The incorporation of solid particles of various types into the rubber mixture, as well as adjustment of the rubber mixture, permits not only that the traction of the tire and its performance life be adjusted, but also permits adjustment of the accumulated drum work and the degree of heat build up in the tire during use. Thus, tires have been proposed for commercial vehicles and trucks whose performance life extends to over 800,000 kilometers, whereby correspondingly relatively hard and wear resistant tread bands are required.
A further disadvantage of conventional tread band applicator devices is that the impact of the tread strips must be renewed with higher precision. Careful follow up labor is required to achieve a relatively acceptable result. Moreover, an undesirable value of the so-called mold filling factor comes into play which leads to a correspondingly greater generation of scraps. This disadvantage should be overcome by the so-called camelback process in which a pre-prepared tread band is applied onto the tire carcass. To be sure, grinding holes occur in connection with this process which then must be filled in a labor intensive operation.
The tread band applicator device described in FR-OS 23 59 700 would not be suitable for producing those tires upon which the high quality demands noted herein are placed.
Numerous other tread band applicator devices have been proposed. EP-A1 637 506 makes note of several patent publications which set forth the state of the art of such tread band applicator devices. A tire retreading device, which operates relatively independently of the given diameter of the tire being handled, is described in DE 42 03 027 and the width of the tread band applied by this device can be adjusted to accommodate the retreading requirements.
It has been known for several years, moreover, to apply tread bands by winding them onto the tire carcass in spiral strips. This manner of applying tread bands was implemented in the 1970s, whereby, for example, DE-PS 17 29 555 describes one such exemplary application of this type. This tread band applying approach is today, however, only infrequently implemented as it cannot be ensured by this approach that air has not been trapped in the applied tread bands. At the same time, the geometry of the tread bands is relatively inexact and the production of a tread band can require up to 5 minutes.
The present invention offers a solution to the challenge of providing a tread band applicator device which is advantageous as well for applying tread bands to tires of large diameter, even if a high performance life of the tire is demanded.
In accordance with the present invention, it is particularly advantageous that the configuration of the press applicator head of the tread band applicator device of the present invention, which moves transversely over the tire carcass to apply the tread band raw material mass, permits the advantages of the known tread band applicator devices to be combined: the press applicator head, which is preferably configured as the extruder itself or as a component of the extruder, can be moved transversely across the outer surface of the tire carcass in such a manner that the tread band strips are circumferentially applied to the tire carcass in thin bands during rotation of the tire carcass. In this manner, the already applied tread band strips act as support for the newly applied tread band strips. In view of the fact that the tread band rubber mixture is relatively hard, a good driving out or expulsion of air results. It is particularly advantageous in connection with this process that the extrusion front, which is formed by the simultaneous pressure and extrusion movement of the tread band raw material mass which has just exited the extruder structure, effectively pushes away the air so that the risk of included or trapped air is foreclosed.
It is particularly advantageous if a side flank of the extruder is formed with a ball or curved shape and if this side flank of the extruder initially leans against the carcass and then, after the beginning of the application of the tread band, leans against the already applied tread band. The thickness of the tread band strips allows for very responsive and precise control of their application by these techniques, whereby, at the same time, it is possible to compensate for any out of roundness areas.
The extrusion of the tread band raw material mass is preferably performed in a manner such that a deliberate over extrusion of the tread band raw material mass is provided which is wrapped around the carcass due to the rotation of the carcass and which is beneficial for a uniform loading of the carcass with the tread band raw material mass.
In accordance with the present invention, it is particularly advantageous if the extruder is pivotable relative to four axes and, in particular, is pivotable relative to five axes. In this manner, it is possible to control the extruder to follow the desired contour of the tire without necessitating an additional capability to adjust the carcass mounting during the tread band applying process.
In accordance with a modified embodiment of the tread band applicator device of the present invention, it is provided that the extruder is configured with a special extruder outlet piece which serves as the press applicator head and is pivotable relative to four or five axes. The extruder of this embodiment of the tread band applicator device of the present invention is connected to the outlet piece via a pressurized conduit.
In accordance with a further modified embodiment of the tread band applicator device of the present invention, it is provided that the extruder is adjustably movable relative to only two or three axes while the carcass mounting as well is limited to adjustable movement relative to a maximum of two or three axes. This embodiment of the tread band applicator device of the present invention likewise permits the desired control of the profile following movement and spacing between the outer surface of the carcass and the extrusion outlet piece.
In accordance with the present invention, it is especially beneficial that the mold filling factor is particularly good. The applied tread bands can be so applied as to effectively correspond exactly to the desired profile so that no excess tread band raw material mass occurs and, consequently, the generation of elastomer scrap which must be discarded is markedly reduced. The method of applying a tread band onto a tire carcass of the present invention also includes the step of moving the press applicator head so as to vary the spacing of the press applicator head from the tire carcass as the press applicator head moves transversely across the tire carcass from an initial relatively greater spacing to a subsequent relatively lesser spacing, whereby the thickness of the tread band raw material mass applied by the press applicator head varies in correspondence with the spacing of the press applicator head from the tire carcass.
Moreover, it is additionally especially advantageous that basically no pre-preparation of a tread band is required so that the overall labor and material effort is to this extent reduced. This also allows the possibility of using high viscosity material for the tread bands such as, for example, Muni 100, which yields correspondingly particularly wear resistant tires. In this connection, it is of advantage that the use of a small nozzle with its corresponding sharp cross section reduction can be dispensed with and that a comparatively large nozzle can be used instead.
It is further provided, in accordance with the present invention, that the press applicator head extends over less than the axial width of the carcass and is mounted for movement in the axial direction. The press applicator head can travel across the so-called xe2x80x9crawxe2x80x9d radius and apply a substantially hard tread band rubber mixture in a targeted manner and in a charge which corresponds to the height of the tread band. The tread band strips, which are applied in adjoining manner to one another, are so hard that they do not cause included or trapped air to adhere to them but, rather, cause such air to be pressed outwardly, whereby it can be advantageous to configure the cross section of the tread band strips generally in a trapezoidal shape with the longer side thereof turned toward the carcass. Due to the pressure of the pressure applying applicator device or of the extruder, each tread band strip is not only pressed against the respective adjoining tread band strip which has already been applied into its position in conjunction with the rotation of the carcass but is also pressed down to the raw radius of the carcass.
The tread band applicator device of the present invention unexpectedly improves the filling in of notches and holes in spite of the use of hard rubber mixtures or rubber mixtures having a considerable solids percentage; evidently, the tread band strip applied by the tread band applicator device of the present invention, which is, for example, one-tenth the width of a tread band, can better follow the outer surface contour and can be pressed thereonto more effectively.
A particularly good advantage of the tread band applicator device of the present invention is that it leads to the result that pressure is exerted only over a small portion of the full width of the carcass. If the same force is brought to bear, then, for example, a ten times larger surface pressure results if the width of the tread band strip is one-tenth of the full axial width of the carcass. At the same time, the carcass is not unreliably distorted and the turning resistance of the press applicator head, which needs to be overcome by the rotational drive of the carcass, is, in any event, not greater than that to be overcome with a conventional press applicator head.
It is to be understood that, in addition to the width of the tread band strips, the type and configuration of the press applicator head or the extruder of the tread band applicator device of the present invention can be accommodated to the tire building requirements. For example, in a modified embodiment of the tread band applicator device of the present invention, two press applicator heads can be moved in opposite directions from one another from a starting position at the axial middle of the carcass in order to thereby build the tread bands toward both sides of the tire. A configuration such as this permits the building of a large tire such as, for example, a tire for a commercial truck, in a markedly short time such as, for example, in 90 seconds.
A second particularly beneficial advantage of the tread band applicator device of the present invention comes from the combination of the tread band strips applied by the tread band applicator device of the present invention with a binder rubber layer. It is provided, in accordance with the present invention, that, a binder rubber layer is applied to the carcass before the application of the tread band strips and after the cushion-to-casing process such as shown, for example, in EP-A1-637,506. A binder rubber layer of this type itself fills in notches or grooves in the carcass. At the same time, the side end regions can be thickened such as can be seen, for example, in FIG. 9 of the just-noted publication. In both cases, the small area increased pressure which results from the tread band application method of the present invention not only improves the pressing of the tread bands onto the binder rubber layer, which thereby improves the connection therebetween, but it also causes a deepening or thickening, in a follow on manner, of the connection between the binder rubber layer and the carcass.
A further particularly beneficial advantage of the tread band applicator device of the present invention is that the tread band applying process can be conducted at comparatively lower temperatures so that it need not be a concern that the binder rubber layer will be prematurely vulcanized before the actual vulcanization of the uncured retreaded tire.